Explosion-proof switch with arc extinguishing gaseous byproduct venting feature and switch contact

Abstract

An electrical switch and switch contact are disclosed, both of which are advantageous for use in an environment containing explosive gases or vapors. The switch housing is designed so that the two joints where explosive gases or vapors can enter or exit into the switch interior can cool any hot gases escaping from the switch interior. Therefore, if any explosive gases or vapors are ignited by an arc in the switch interior, they are cooled during their exit from the switch, so that they cannot ignite the explosive environment outside the switch. This is done using a labyrinthine path between the two switch housing members, and a lengthy metal-to-metal, metal-to-ceramic, or ceramic-to-ceramic path between the switch actuator and the switch housing. The contact is designed such that it has a greater flexural length, without requiring a substantial increase in the housing body volume. This allows a smaller amount of hazardous gas or vapor to come into contact with a potential arc. The contact design allows a good degree of overtravel and a contact cleaning action, both of which contribute to the reliability of the electrical connection made by the switch.

What is claimed is: 
     
       1. An electrical switch comprising: upper and lower housing portions;   an actuator shaft protruding out of one of the upper or lower housing portions;   stationary electrical contacts in both the upper and lower housing portions;   a resilient movable electrical contact attached to the actuator shaft and movable by the actuator shaft from a position contacting the stationary electrical contacts in the upper housing portion to a position contacting the stationary electrical contacts in the lower housing portion;   wherein the area between the upper and lower housing portions is characterized by a joint sufficiently long to cool any hot gases escaping from the interior of the switch, and the joint between the actuator shaft and the housing portion from which the actuator shaft protrudes is also characterized by a joint sufficiently long so as to cool any hot gases escaping from the interior of the switch;   and wherein at least a portion of the movable contact is substantially parallel to the direction of movement of the actuator shaft.   
     
     
       2. The electrical switch of claim 1, wherein: the actuator shaft slides within a tubular bearing, constructed of a metal or ceramic material, in the housing portion from which the actuator shaft protrudes.   
     
     
       3. The electrical switch of claim 1, wherein: the joint between the upper and lower housing portions is a labyrinthine path.   
     
     
       4. The electrical switch of claim 3, wherein: the labyrinthine path is constructed of mutually enmeshing ridges and valleys on the upper and lower housing portions.   
     
     
       5. The electrical switch of claim 1, wherein: the actuator shaft is spring biased into contact with the stationary contacts in one of the housing portions.   
     
     
       6. The electrical switch of claim 1, wherein: the actuator shaft protrudes from the upper housing portion;   a portion of the actuator shaft is disposed in a volume of the interior of the upper housing portion extending above the stationary contacts in the upper housing portion; and   at least half of the length of the movable contact is contained within said volume of the interior in which the actuator shaft is disposed when the movable contact is in contact with the stationary contacts in the upper housing portion.   
     
     
       7. The electrical switch of claim 1 wherein: the movable contact is constructed of a sheet of electrically-conductive metallic material.   
     
     
       8. The electrical switch of claim 1 wherein: the movable contact comprises two L-shaped arms and a cross-piece connecting the two L-shaped arms at one end of each of the L-shaped arms.   
     
     
       9. The electrical switch of claim 8 wherein: the cross-piece is arranged perpendicularly to the one end of both the L-shaped arms.   
     
     
       10. The electrical switch of claim 9 wherein: the cross-piece and L-shaped arms are constructed of an electrically conductive material such that when force is applied to the cross-piece after the other ends of the L-shaped arms are in contact with one of the stationary contacts the L-shaped arms flex across the stationary contact.   
     
     
       11. The electrical switch of claim 10, wherein: contact buttons are affixed to the other end of the L-shaped arms.   
     
     
       12. The electrical switch of claim 11, wherein: contact points are affixed to the stationary contacts.   
     
     
       13. The electrical switch of claim 12, wherein: the contact buttons are wiped across the contact points when the L-shaped arms flex.   
     
     
       14. An electrical switch comprising: an upper housing portion comprising: two terminal contacts;   two stationary contacts electrically connected to a respective one of the terminal contacts;   an upstanding portion enclosing an interior volume above the stationary contacts;   a tubular metallic or ceramic bearing within the upstanding portion;   at least one ridge and at least one valley on the lower extremity of the upper housing portion;     a lower housing portion comprising: two terminal contacts;   two stationary contacts electrically connected to a respective one of the terminal contacts;   at least one ridge and at least one valley on the upper extremity of the lower housing portion constructed to enmesh with the at least one ridge and at least one valley on the lower extremity of the upper housing portion;     a movable contact contained between the upper and the lower housing portions comprising: two L-shaped arms;   a cross-piece connecting the two L-shaped arms at one end of each of the L-shaped arms;   contact buttons affixed to the other end of the L-shaped arms;   wherein the cross-piece is arranged perpendicularly to the one end of both the L-shaped arms, and the cross-piece and L-shaped arms are constructed of a resilient, electrically conductive material, such that when force is applied to the cross-piece after the other ends of the L-shaped arms are in contact with said stationary contacts in said upper housing or said stationary contacts in said lower housing, the L-shaped arms flex across said stationary contacts;     an actuator in engagement with said movable contact;   said actuator having an outer face of a metallic or ceramic material, said actuator sliding in said bearing, and said actuator being in engagement with said movable contact; and   a spring in engagement with said lower housing and said actuator;   wherein at least one arm of said L-shaped arms extends substantially within said interior volume when said movable contact is in engagement with said stationary contacts in said upper housing.